We have developed a unique model system for passive serum immunotherapy where immunological management of a highly lethal tumor, the ascites form of murine adenocarcinoma 755a, can be carried out reproducibly and with remarkable efficiency. Information concerning the mechanism of AD755a immunotherapy will be obtained through the isolation and characterization of the AD755a tumor-associated antigens and the serum factors responsible for providing protection. The type-C oncornavirus associated with the AD755a tumor will be isolated and the role of its structural polypeptides in the process will be determined. The identity of AD755a tumor surface antigen(s) which induced and/or react with the protective serum will be analyzed by several analytical immunoassays, and attempts will be made to produce a protective serum using purified AD membrane antigens. The nature of the protective serum factor will be determined by isolating the class and subclass of antibody responsible for protection and the possible role of anti-idiotype antibodies in the serum will be analyzed.